Pad Cratering: The Basics

Pad cratering, what is it?  Pad cratering is defined as a separation of the pad from the PCB resin/weave composite or within the composite immediately adjacent to the pad.  It triggers failures only if the crack propagates into a copper trace or conduction pad makes the circuit open or intermittent.

Pad Cratering Drivers:

  • Finer pitch components
  • More brittle laminates (lead-free compatible)
  • Stiffer solders (SAC vs. Sn Pb)
  • Presence of large heat sinks
  • Location
  • PCB Thickness
  • Temperatures and cooling rates

Issues with Detecting Pad Cratering

  • Companies are frequently unaware until failure occurs
    • Recalls can be frequent and painful 
  • Potential Warning Signs
    • Excessive BGA repair rates
    • High percentage of “defective” BGA’s
    • High rate of “retest to pass” at in circuit test (ICT)
  • Difficult to detect using standard procedures of X-ray, generally must use destructive testing such as dye n pry, ball shear, and ball pull
  • Expensive advanced testing methods now available to screen for pad cratering

“Band Aid” Solutions for Pad Cratering

Solutions to prevent costly damage are labor intensive, costly, or have marginal impact on the problem.

  • Expoxy fillets at BGA corners
    • Ineffective and do not prevent board flexing
  • Increase board thickness to eliminate flexing
    • Expensive
  • Changing BGA and PCB pad design
    • Limited effectiveness, limits design and sources of components, can be expensive
  • Underfill of BGA components
    • Labor intensive, prevents rework of BGA parts after assembly

Zeta Cap as a solution

 

How does it work?

  • Zeta Cap requires no special processing or equipment.  It simply replaces the outer layer foil in the PCB construction
  • When used as a cap layer, it becomes the interface between the copper pad and the rest of the PCB
  • The more pliant cap will prevent or block fractures and protect copper connections (traces) the the pad

Why does it work?

It serves as a barrier to block pad cratering with a unique combination of properties:

  • High strength without being brittle
  • Modulus allows for some flexibility
  • Very high Tg and Td
  • Very low CTE (close to copper and solder)
  • Halogen free
  • Lead free compatible
  • Used on PCB surface with convention materials

If you are interested in learning more, please contact us for additional information.  Material spec sheets and test and reliability data are readily available! 

 

Purchasing and designing printed circuit boards does not have to be difficult! 

 

A special thank you to Insulectro for working with us and compiling this information! 

 

  

PCB Material Data Sheets

For all of our friends that feel just a little uncertain when material data sheets are discussed and words like dielectric constant, Tg and  coefficient of thermal expansion are thrown into the discussion, we have compiled a short cheat sheet just for you.

Dk – Dielectric Constant – The way the electrical signal moves through the material from front to back.
Dissipation Factor – Loss Tangent – How much the signal dissipates or “leaks” out of the substrate.  The higher the speed, the higher the losses.
Coefficient of Thermal Expansion – Thermal fractional change in material for unit change in temperature.
Resistivity:  How strongly the material resists a current.
Tensile Strength:  Relates to the rigidity of the material as well as the peel strength.  How far can the material be stretched before permanent damage occurs.
Dimensional Stability:  The tendency of material  to change in the x and y dimensions when copper is etched away from the dielectric material or when exposed to temperature extremes.
Tg – Glass Transition Temperature – Temperature that material exhibits a change in physical characteristics. The resin changes from rigid or hard to a soft, rubber like material.
Td  – Thermal Decomposition Temperature – Temperature at which the material weight changes by 5%.  This parameter determines the thermal survivability of the resin material.
 
As always, if you have questions or would like additional information, please contact us!
Purchasing and designing printed circuit boards does not have to be difficult!

Benefits of a fine line additive PCB process

The traditional subtractive etch process for manufacturing printed circuit boards becomes much less reliable when working with features that are sub 1 mil.  There has been a new additive process developed that uses a precursor ink to break through these barriers and meets four market needs:

Image

1.  Fine line (< 25 micron) Additive (Rigid and flex PCB)

  • Precursor ink makes the additive process practical
  • Additive process makes the fine lines practical
  • This process works well with existing manufacturing equipment
  • Cost savings over conventional processing can be 35%-60%

2.  Via excellence (Rigid PCB)

  • Precursor ink is the key advantage
  • Reduces electroless usage by 60% or more
  • Reduces the use of water by 60% or more
  • Lower cost than conventional processing

3.  Stacked microvia excellence (Rigid/Flex PCB)

  • Better results than conventional processing
  • Precursor ink is the key advantage
  • Eliminates the need for sequential lamination
  • Cost savings can be 20%-30%

4.  Selective via plating (Multilayer rigid PCB)

  • Precursor ink and ink blocker are the keys
  • Eliminates the need for sequential lamination processing
  • Cost savings can be 20%-60%

This process can be used as a stand-alone technology or in conjunction with the traditional subtractive etch process.  Please contact us if you are interested in learning more!

www.omnipcb.com

Flex Circuit Shielding Options

Shields are often needed when an application requires limits in electromagnetic interference/radio frequency interference (EMI/RFI)  or to fabricate low-voltage circuitry.  Shields are material around a conductor or a group of conductors that limit these factors.

 

 There are several options to consider with flexible circuits:

 

 Solid Copper:  Solid copper is the most common method of shielding.  Copper shield can be put on one or both sides of the circuit.  Solid copper can also cover selective conductors.  Solid copper shields increase the rigidity of the circuit, and should be included in the thickness to bend radius ratios.

 

 Crosshatched Copper:  Crosshatching is an artwork design that relieves much of the copper shield areas by the use of a pattern.  Crosshatch shielding can also cover selective conductors.  It helps the circuit to retain its flexibility and can be put on one or both sides.

 

 Conductive Silver:  Conductive silver can be substituted for copper for shielding purposes in some applications.  Silver can be a solid or crosshatched shield and can be put on one or both sides of the circuit.  It can also cover selected conductors only.  Silver shielding is not recommended for dynamic flexing applications due to its brittle characteristic, and may be prone to cracking in severe bending applications.

CONTACT US with any flex or rigid flex design questions.  We are here to help! 

 

  www.omnipcb.com

.4 mm device routing – PCB

Here is an example for routing a .4 mm pitch device:

Streamline .4mm device routing

Outer Layer With Quadrant Dog bone

DUT Pad .25mm

Via Pad .2mm

Laser Via .125mm

Trace

.1mm, .125mm, .175mm

Contact us for additional information:  http://www.omnipcb.com

Tara Dunn, 507-332-9932, tarad@omnipcb.com

Circuitry on a balloon catheter

Advantage to Additive Fine Line PCB manufacturing process:

Medical Device: Circuits on balloon catheter
Need: fine line and spaces (<25 µm) on flexible substrate
Benefit: Reduces cost by integrating circuit function with catheter function
§Unit size is about 1 cm X 2 cm
2 µm copper, single sided
10 µm lines and spaces
Contact us to learn more!  www.omnipcb.com
Tara Dunn, 507-332-9932, tarad@omnipcb.com

IPC and MIL SPEC for Printed Circuit Boards

There are two types of specs commonly used in the PCB industry: IPC and the MIL Spec. Here is a handy reference guide:

IPC-SPECS:

  • IPC-6013 – Qualification and Performance Specification for Flexible Printed Boards
  • IPC-T-50 – Terms and Definition
  • IPC-MF-150 – Metal Foil for Printed Wiring Applications
  • IPC-FC-231 – Flexible Bare Dielectrics for Use in Flexible Printed Wiring
  • IPC-FC-232 – Specification for Adhesive Coated Dielectric Films For Use as Cover Sheets for Flexible Printed Wiring
  • IPC-FC-241 – Flexible Metal Clad Dielectrics for use in Fabrication of Flexible Printed Wiring
  • IPC-SM-840 – Qualification and Performance of Permanent Solder Mask
  • IPC-2221 – Generic Standard on Printed Board Design
  • IPC-2223 – Sectional Design Standard for Flexible Printed Boards
  • IPC-4101 – Laminate/Prepreg Materials Standard for Printed Boards
  • IPC-6011 – Generic Performance Specification for Printed Boards
  • IPC-6012 – Qualification and Performance Specification for Rigid Printed Boards
  • J-STD-001 – Requirements for Soldered Electrical and Electronics Assemblies
  • J-STD- 002 – Solderability Tests for Component Leads, Terminations, Lugs, Terminals and Wires
  • J-STD-003 – Solderability Tests for Printed Boards
  • J-STD -004 – Requirements for Soldering Fluxes
  • J-STD- 005 – General Requirements and Test Methods for Electronic Grade Solder Paste
  • J-STD-006 – General Requirements and Test Methods for Soft Solder Alloys and Fluxed and Non-Fluxed Solid Solder for Electronic Soldering Applications

MIL-SPECS

  • MIL-P-50884 – Flex Manufacturing and Performance
  • MIL-STD-2118 – Flex Design Standard
  • MIL-STD-105 – Sampling Procedures and Inspection Tables
  • MIL-STD-129 – Marking for Shipment and Storage
  • MIL-STD-130 – Identification for Marking
  • MIL-STD-202 – Test Methods for Electronic Equipment
  • MIL-STD-2000 – Soldering and Assembly
  • MIL-STD-45662 – Calibration System Requirements
  • DOD-D-1000 – Engineering Drawings
  • DOD-STD-100 – Engineering Drawing Practices
  • ANSI-Y-145 – Dimensioning and Tolerancing
  • MIL-S-13949 – Plastic Sheet, Laminate, Metal Clad (for PWB’s)
  • MIL-C-14550 – Copper Plating (Electrodeposited)
  • MIL-I-43553 – Ink Marking, Epoxy Base
  • MIL-G-45204 – Gold Plating (Electrodeposited)
  • MIL-I-45208 – Inspection System Requirements
  • MIL-Q-9858 – Quality Program Requirements
  • MIL-P-81728 – Plating Tin Lead (Electrodeposited)
  • MIL-P-55110 – Printed Wiring Boards
  • QQ-N-290 – Nickel Plating (Electrodeposited)

Please contact us with any questions!  Omni PCB – Your PCB Advisors   www.omnipcb.com